Plasma arc torches are used for cutting metal material by directing a stream of ionized gas particles toward a work piece. The operation of a conventional plasma torch is described, for example, in U.S. Pat. No. 3,813,510. In the conventional plasma torch, a gas is supplied through an internal passage toward the front end of the torch body, where it is directed in front of an electrode which has a negative charge. Imbedded within the electrode is an insert. Adjacent to the front end of the electrode is a nozzle which is electrically connected to a high voltage source. The nozzle has an axial opening toward the front end of the torch and is electrically insulated from the electrode. When a sufficiently high voltage is applied to the nozzle, an arc jumps from the nozzle to the electrode. The arc heats the gas, which becomes ionized and exits through the axial opening in the nozzle. As the torch is moved closer to the work piece, the arc jumps from the insert in the electrode to the work piece.
In conventional plasma arc torches, the nozzle is nested in an anode which is electrically connected to the high voltage source. The anode of the conventional plasma arc torch is an integral part of the torch and cannot be readily removed or replaced. This feature of the conventional plasma torch is problematic. When the conventional torch is operating, a high voltage is supplied from the electrical connector through the anode and to the nozzle. It is necessary that the nozzle has a good electrical connection with the anode. The nozzle itself is consumed during the operation and frequently requires replacement. There are a number of reasons why after the replacement of the nozzle a small gap between 0.001 and 0.010 inches can be present between the nozzle and the anode. For example, the operator does not tighten firmly enough the enclosure which holds the nozzle or that the enclosure is worn out and cannot press the nozzle firmly onto the seating surface on the anode. Another reason is that during the replacement of the nozzle, particles of dirt from the environment may become trapped on the seating surface between the nozzle and the anode. When this occurs, the voltage supplied to the anode arcs across the gap, damaging the anode. Because the conventional anode is an integral part of the torch body, however, the anode itself cannot be removed or replaced without damaging the torch body. Consequently, even though damage may be limited only to the anode, the entire torch body must be replaced.
The conventional plasma arc torch thus presents a number of disadvantages. One disadvantage is that the useful life to the conventional torch is limited to the life of the anode. Another disadvantage of the conventional torch is that the anode cannot be readily removed for repair or replacement. Another disadvantage is that the cost of maintaining the conventional torch is increased because a torch user cannot simply replace the anode but must instead replace the entire torch.